Well here's a few thoughts/comments for your consideration.
First, being a member of the bi-focal crowd, I find it best for repair work to get a pair of cheap "granny-style" non-prescription reading glasses and move them up to the bridge of your nose. That way when your head is sideways you get the proper magnification and a full field of view. Bi-focals only good when head is vertical.
I too was unfamiliar with the term "check strap" as I had always known these devices as "hill-holders". Interesting that my '98 Ford service cd does use the term "check strap" whereas my '97 Ford service manual refers to them as "door stops". In better quality cars (e.g. Buick) these devices not only limit door swing, but also have a spring cam roller detent mechanism that prevents a door closing (due to its own weight) when you are on a slight upgrade. Cheaper cars (e.g. Firefly and Contiques) only seem to provide the means to restrict the door swing.
In regards to your specific problem, I personally use spray white lithium grease on the door hinges and the inner/outer pins of the check straps. You have to remove inner door panel to remove check strap but that is not necessary for lubrication (the inner and outer ends are similar construction). I find the rear driver's side door the stiffest door to operate, but that is the one that gets the least amount of use.
